1. Field of the Invention
The present relates to a semiconductor light emitting device of a surface emitting type using photonic crystal grown on a substrate and a method of fabricating the same.
2. Description of the Related Art
The conventional semiconductor light emitting devices using photonic crystal are disclosed in, for example, Japanese Laid-Open Patent Application Publication No. Hei. 11-330619, Japanese Laid-Open Patent Application Publication No. 2001-308457, Japanese Laid-Open Patent Application Publication No. 2001-9800 (U.S. patent Publication No. 2002/0109134 specification), Japanese Laid-Open Patent Application Publication No. Sho 63-205984 (U.S. Pat. No. 4,847,844 specification), and Japanese Laid-Open Patent Application Publication No. 2002-062554.
Likewise, the semiconductor light emitting device is also disclosed in “Imada et al., Applied Physics Letters 75 (1999) 316 (Appl. Phys. Lett. 75 (1999) 316).” FIG. 1 is a perspective view showing a structure of the conventional semiconductor light emitting device using photonic crystal disclosed in this “Imada et al.” As shown in FIG. 1, on a n-type InP substrate 51, a n-type InP photonic crystal layer 52, a n-type InP lower cladding layer 53, a quantum well active layer 54 comprised of InGaAsP, and a p-type InP upper cladding layer 55 are sequentially disposed. On a rear surface of the n-type InP substrate 51, a lower electrode 57 is formed, and on a front surface of a p-type InP upper cladding layer 55, a circular upper electrode 56 having a diameter of approximately 350 μm is formed. Further, on a n-type InP photonic crystal layer 52, a plurality of circular concave portions 59 each having a diameter of 0.2 μm are periodically formed.
The n-type InP photonic crystal layer 52 is grown on the n-type InP substrate 51 to have the plurality of concave portions 59, while the p-type InP upper cladding layer 55, the quantum well active layer 54, and the n-type InP lower cladding layer 53 are grown in this order on another substrate. Then, the n-type InP lower cladding layer 53 is brought into surface contact with the n-type InP photonic crystal layer 52, and they are annealed in hydrogen atmosphere to be fusion bonded to each other (see arrow 60). Thereafter, the substrate is removed from the substrate and the p-type InP upper cladding layer 55 grown thereon, the circular upper electrode 56 is formed on a surface thereof, and the lower electrode 57 is formed on the rear surface the n-type InP substrate 51, thereby fabricating a semiconductor light emitting device structured as described above.
Upon conducting a current between the upper electrode 56 and the lower electrode 57 in the semiconductor light emitting device fabricated as described above, at a threshold current of 2A or more, stimulated emission is observed and a single mode with an oscillation wavelength of 1.3 μm is gained. Light emits from an outer peripheral portion 58 of the upper electrode 56.
As should be understood, in the conventional semiconductor light emitting device, the threshold current is relatively large, for example, 2A.
In addition, since the upper electrode 56 is circular, polarization planes of light have different directions. The polarization planes may be oriented in the same direction by forming the concave portions 59 in the shape of oval, but the plurality of concave portions 59 which have the same oval shape are very difficult to create.
Even in the light having the same polarization plane, the light emitting wavelength becomes unstable because of the presence of two stable light emitting modes.
Although the semiconductor light emitting device is fabricated by fusion bonding crystals to each other as described above, the entire surfaces of the substrates having a large diameter are difficult to fusion bond.